she used paint, Michaels (pretty much our version of hobby lobby I guess) has paint that can be used for this purpose. I've also heard it marbling paint, do a google search and there are a few videos of people doing it
I was at a show fair last summer and I saw something really cool, a leather worker was selling wallets and trays and the like and they had a marble pattern on them. I asked how it was done and she used the same method that people use to marble paper for book binding. The results were awesome
My Dad used to raise Bull Terriers and they will test for the alpha male spot in the house. They were bred to fight and immense personality. Great dogs but not for the faint of heart.